1. Field of the Invention
The present invention relates to a polymer of a water-soluble radical-polymerizable monomer, a process producing the polymer and a flocculant comprising the polymer. More particularly, the present invention relates to a polymer of a radical-polymerizable monomer which has a narrow molecular weight distribution, has nitroxy group at the end of the molecule and is useful as a flocculant in the dewatering treatment of organic sludge, a process for producing the polymer in accordance with the living radical polymerization and a flocculant comprising the polymer.
2. Description of Related Art
In recent years, organic sludge containing biologically treated sludge which is formed from city waste water or by the sewage treatment has problems in that the amount of dewatering agents necessary for dewatering is increasing due to the increase in the amounts of organic substances and putrefaction and that the amount of the sludge treatment cannot be increased due to the increased content of water in the dewatered cake of sludge and dewatering sludge becomes more difficult. To dewater sludge which is not easily dewatered, various processes have been attempted and it is known that addition of organic macromolecular flocculants is effective.
For example, in Japanese Patent Application Laid-Open No. Showa 63(1988)-158200, as a process for dewatering sludge which can decrease the content of water in the dewatered cake and facilitates separation of the dewatered cake from a filter cloth, it is proposed that an inorganic flocculant is added to organic sludge, then an amphoteric organic macromolecular flocculant is added to the organic sludge which has a pH of 5 to 8 and the resultant sludge is dewatered. In Japanese Patent Application Publication Heisei 6(1994)-239, as a process for dewatering organic sludge which has a great capacity of the sludge treatment, shows a high recovery of suspended solids, facilitates separation of dewatered cake from a filter cloth and can decrease the content of water in the dewatered cake, it is proposed that an inorganic flocculant is added to the organic sludge, then an amphoteric macromolecular flocculant having a specific colloid equivalent value and a specific ratio of the amount of the anion to the amount of the cation is added to the organic sludge and the resultant organic sludge is dewatered. However, these processes have drawbacks in that a great amount of chemicals must be used and cost of the treatment increases, that the type of sludge to which the process is advantageously applied is limited and that apparatuses and operations are complicated.
Therefore, a flocculant which can be applied widely to organic sludge containing biologically treated sludge which is formed from city waste water and industrial waste water and by the sewage treatment, achieves effective dewatering by addition in a small amount, forms flocks having great strength and provides cake having a small water content, has been desired.
The present invention has an object to provide a polymer of a water-soluble radical-polymerizable monomer which has a narrow molecular weight distribution, has nitroxy group at the end of the molecule and useful as the flocculant in the dewatering treatment of organic sludge; a process for producing the polymer by the living radical polymerization; and a flocculant comprising the polymer.
As the result of extensive studies by the present inventors to overcome the above problems, it was found that a polymer of a water-soluble radical-polymerizable monomer having a narrow molecular weight distribution exhibits excellent properties as the organic macromolecular flocculant and that such a polymer can be produced by the living radical polymerization of a water-soluble radical-polymerizable monomer in an aqueous solution in the presence of a nitroxy radical. The present invention has been completed based on the above knowledge.
The present invention provides:
(1) A polymer of a water-soluble radical-polymerizable monomer which has nitroxy group at an end of a molecule;
(2) A process for producing a polymer of a water-soluble radical-polymerizable monomer which comprises polymerizing the water-soluble radical-polymerizable monomer in a presence of a polymerization initiator in an aqueous solution containing a nitroxy radical;
(3) A process described in (2), wherein the nitroxy radical is di-t-butylamineoxy radical, 2,2,6,6-tetramethyl-1-piperidinyloxy radical or 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy radical;
(4) A process described in (2), wherein the nitroxy radical is insoluble in water and dispersed in an aqueous solution by dissolving the nitroxy radical into an organic solvent, followed by adding an obtained solution to the aqueous solution;
(5) A process described in (2), wherein the water-soluble radical-polymerizable monomer is a vinyl monomer soluble in water;
(6) A process described in (2), wherein the water-soluble radical-polymerizable monomer is a diallyldialkylammonium halide;
(7) A process described in (2), wherein the polymerization initiator is a redox polymerization initiator;
(8) A process described in (2), wherein the polymerization initiator is a salt of peroxodisulfuric acid;
(9) A process described in (2), wherein the nitroxy radical is present in an amount of 0.01 to 2 moles per 1 mole of the polymerization initiator;
(10) A process described in (2), wherein a polymerization temperature is 10 to 60xc2x0 C.; and
(11) A flocculant which comprises a polymer of a water-soluble radical-polymerizable monomer produced in accordance with the process described in (2).